Wow for those who dont understand wireless, know this: Full duplex on the same frequency is in fact, undone at this point in the market. Currently, there is ONE way to achieve a full duplex radio transmission: Use 2 frequencies.
That said, are there some things that seem full duplex? Certainly. WiFi for one. However, the AP and the clients are never talking at the exact same time. Time in this case being very small, so the transition goes unnoticed. Real example a 802.11n AP at HT40 is a max 300Mbit link. With really great equipment, you can get very close to 300mbit in one direction. Do a full duplex transmission, and it will get around 150 up, and 150 down.. close to the actual 300.. This is because now the AP is trying to send, and so is the client, so they have to take turns. Thus, a 50% reduction in non-aggregated throughput, but still an aggregate equalling the maximum of the technology.
With the technology outlined above, said WiFi could theoretically send 300mbit, and receive 300mbit at the same time. Raising the aggregated bandwidth to 600 (albeit that you wont get 600 in ONE direction). Effectively doubling it.
MIMO antenna arrays currently make a difference by changing the polarity and using a different modulation point for transmission, but are still not full duplex. In the case of cellular companies, if they used this, they could handle double the traffic in a given area, with the same spectrum allocation they currently have, which in this case would help AT&T more than acquiring T-Mobile as far as spectrum is concerned.